The invention relates to articles and methods for scavenge oxygen in packages containing oxygen-sensitive products, in particular food and beverage products.
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and xe2x80x9cshelf-lifexe2x80x9d of the product. By limiting the oxygen exposure of oxygen sensitive products in a packaging system, the quality of the product is maintained and spoilage or damage due to oxygen contamination is avoided. In addition such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
There are two main sources of oxygen contamination in a package: the head space oxygen and ingress oxygen. The head space oxygen is the oxygen remaining in the package after the product has been sealed off within packaging materials. Ingress oxygen is the oxygen which diffuses directly through the package walls or enters the package through voids or holes in the package (particularly at the seals). Contamination by head space oxygen occurs only when the package is initially sealed. By contrast, the ingress oxygen enters the package slowly from the time the package is sealed until it is opened by the consumer. Over time, a substantial amount of oxygen may enter the package as ingress oxygen. It is therefore desirable to remove the relatively small amount of head space oxygen quickly, before the high oxygen concentration can damage or degrade the packaged product, and to remove ingress oxygen more slowly but continuously while the package is on the shelf, to prevent a significant buildup of oxygen over time. A package capable of quickly removing head space oxygen and absorbing ingress oxygen over time would provide significant protection for oxygen-sensitive products.
In the food packaging industry, several means for limiting oxygen contamination in a packaged product have been developed. For example, products may be packaged under a modified atmosphere (called xe2x80x9cmodified atmosphere packagingxe2x80x9d or MAP), or packaged in a vacuum. In these techniques, reduced oxygen environments are employed in the packaging process which reduce or eliminate contamination from head space oxygen. However, MAP or vacuum packaging processes are costly and do not prevent later contamination from ingress oxygen. In fact, a package with a partial or full vacuum would likely increase the oxygen permeation rate of the package walls.
In barrier film packaging processes, materials are used in the package walls which physically prevent oxygen from entering the package interior. Such processes, however, do not prevent contamination by head space oxygen, or prevent ingress of oxygen from holes or voids in the package seals. Furthermore, making a package wall completely impermeable to oxygen is often prohibitive, for example, in increased cost of materials and the unacceptably high weight and rigidity of the package. Therefore, a commercially viable package will typically have some degree of contamination from ingress oxygen.
Another means for limiting oxygen exposure in a package involves incorporating an oxygen scavenger in the packaging structure. An oxygen scavenger is a substance that consumes, depletes, or reduces the amount of oxygen from a given environment.
For example, an oxygen scavenging material may be included within the package cavity as a sachet. Insertion of sachets requires additional operations in the packaging process, thus increasing cost and production time. Sachets also take up space normally occupied by product. And while sachets may be effective at scavenging head space oxygen, they cannot stop ingress oxygen from entering the package and contacting the product before being scavenged. Furthermore, the use of sachets causes safety concerns, as the end-user may inadvertently consume the sachet along with the packaged product.
Alternatively, an oxygen scavenger may be incorporated into the packaging structure itself, for example by constructing the package walls with an oxygen scavenging polymer. Previous packaging systems incorporating oxygen scavenging materials use only one such material in a given package, thus producing a package with homogeneous oxygen scavenging properties.
U.S. Pat. No. 5,211,875 to Speer et al. discloses oxygen scavenger compositions comprising substituted or unsubstituted ethylenically unsaturated hydrocarbon polymers and a transition metal catalyst, which are activated on exposure to actinic radiation or an electron beam. These compositions are used to construct food packaging material with uniform oxygen scavenging properties.
U.S. Pat. No. 5,639,815 to Cochran et al. discloses a package wall comprising a single composition of an oxidizable polymer and a transition metal catalyst. The polymer/catalyst composition acts as an oxygen scavenger, and thus the package wall has homogeneous oxygen scavenging properties.
U.S. Pat. No. 5,700,554 of Speer et al. discloses an article useful for packaging oxygen-sensitive products, which contains an ethylenically unsaturated hydrocarbon polymer and a transition metal salt catalyst. Again, a given article contains only a single polymer/catalyst composition, and thus the oxygen scavenging properties of the package are homogeneous.
U.S. Pat. No. 5,776,361 to Katsumoto et al. discloses an oxygen scavenging composition or system for use in packaging oxygen-sensitive products, comprising at least one polyterpene and at least one catalyst. These packages also employ a single polyterpene composition in a given package, producing packages having homogeneous oxygen scavenging properties.
The packages disclosed in the U.S. Patents listed above may be engineered to have certain overall oxygen scavenging properties, so that either (but not both) the head space oxygen or ingress oxygen is optimally removed. Alternatively, materials with intermediate oxygen scavenging properties may be used in a given package to simultaneously combat both head space oxygen or ingress oxygen contamination, resulting in the suboptimal removal of oxygen from either source. What is needed, therefore, is a package with differential oxygen scavenging properties, which allows for the effective removal of both head space and ingress oxygen.
xe2x80x9cHead space oxygenxe2x80x9d is the oxygen remaining in the package after the product has been sealed within the packaging materials.
xe2x80x9cIngress oxygenxe2x80x9d is the oxygen which diffuses directly through the package walls or enters the package through voids or holes in the package.
xe2x80x9cOxygen scavengerxe2x80x9d or xe2x80x9coxygen scavenging materialxe2x80x9d is a substance that consumes, depletes or reduces the amount of oxygen from a given environment.
xe2x80x9cOxygen scavenging capacityxe2x80x9d (hereinafter xe2x80x9ccapacityxe2x80x9d) is the total amount of oxygen consumed per unit mass of scavenging material. Typical units of capacity are cubic centimeters (cc) of oxygen per gram of material.
xe2x80x9cOxygen scavenging ratexe2x80x9d (hereinafter xe2x80x9cratexe2x80x9d) of an oxygen scavenging material is the amount of oxygen consumed per unit time per unit mass of scavenging material. Typical units of rate are cc/g/day.
xe2x80x9cHigh rate oxygen scavenging materialsxe2x80x9d or xe2x80x9chigh rate materialsxe2x80x9d are oxygen scavengers chosen or designed to scavenge head space oxygen. xe2x80x9cLow rate oxygen scavenging materialsxe2x80x9d or xe2x80x9clow rate materialsxe2x80x9d are oxygen scavengers chosen or designed to scavenge ingress oxygen. Although generally high rate materials scavenge oxygen at faster rate than low rate materials, it is understood that there may be some overlap in the rates of high and low rate oxygen scavenging materials.
xe2x80x9cOxygen permeation ratexe2x80x9d or xe2x80x9coxygen permeancexe2x80x9d is the rate of diffusion of oxygen through a package wall at a certain pressure as measured in the absence of oxygen scavenging. Typical units of oxygen permeance are cc/[m2 atm day].
In one aspect of the invention, there are provided packages for oxygen-sensitive products comprising at least two oxygen scavenging materials with different oxygen scavenging properties. The oxygen scavenging properties of each oxygen scavenging material include rate and capacity. Either the rate, capacity, or both may differ between the oxygen scavenging materials comprising the packages of the invention.
In one embodiment, the oxygen scavenging materials in the package comprise at least one high rate material for absorbing head space oxygen, and at least one low rate material for absorbing ingress oxygen. Preferably, the high rate material has a rate that is significantly greater than the rate of oxygen absorption by the packaged product, and a capacity capable of consuming substantially all the oxygen in the head space. The low rate material preferably has a rate at least equal to the rate of oxygen permeation rate of the package, and a capacity approximately equal to the product of 1) the oxygen permeation rate of the package, 2) the total area of the package, and 3) the expected shelf life of the package.
In another aspect, at least one high-rate oxygen scavenger is arranged in the package so as to scavenge head space oxygen, and at least one low-rate oxygen scavenger is arranged in the package so as to scavenge ingress oxygen. In one embodiment, the package is in laminate (i.e., multiple layer) form and comprises at least one layer of high rate material for absorbing head space oxygen and at least one layer of low rate material for absorbing ingress oxygen. Preferably, at least one layer of high rate material is placed nearer to the internal void of the package (i.e., nearer to the product) than the low rate material, and at least one layer of low rate material is placed nearer to the outside of the package than the high rate material.
In another aspect of the invention, the packages may comprise more than one high rate material and/or more than one low rate material, in any arrangement which allows effective absorption of head space and ingress oxygen.
Any adjustable-rate oxygen scavenging material may be used in the packages of the invention, for example compositions comprising one or more oxidizable organic polymers and a metal catalyst. Radiation-activatable compositions comprising oxidizable organic polymers and metal catalysts are preferred.
In another aspect, the invention provides methods of constructing packages having differential oxygen scavenging properties in which a film comprising at least one high rate material and at least one low rate material, optionally together with other layers, is formed into a package.
A multilayer film for constructing differential oxygen scavenging packages of the invention is also provided, comprising at least one high rate material and at least one low rate material optionally together with other layers.
In a further aspect of the invention, there are provided methods of protecting oxygen-sensitive products from damage or degradation due to oxygen contamination, by packaging the products in an article comprising at least two oxygen scavenging materials with different oxygen scavenging properties.